The goal of this project is to use flicker and flicker interactions to understand more about vision and visual perception. A common theme throughout is the combination of measures of flicker sensitivity and flicker delay (between signals generated by different receptor types or by the same receptor types but in different eyes) to reveal the inner workings of the visual system. Two related areas of study are proposed: (I) Organization of the early visual system The phase delays and amplitudes of the middle-wavelength (M) and long- wavelength (L) cone inputs to the channel(s) that signal flicker will be systematically analyzed under various adaptational conditions. Preliminary evidence shows that the data can be modeled by assuming that slow (+MS-LS or +LS-MS) as well as fast (+Mf+Lf) cone signals feed into the achromatic channel ( - means inverted in sign, + non-inverted, f fast and s slow). (II) Light adaptation of the visual system Measures of the delay between flicker signals generated by the two eyes under different states of adaptation will be combined with measures of flicker sensitivity to characterize the effects of light adaptation more completely than has been done before. Armed with this newly won information, we will critically evaluate current models of light adaptation and develop new ones. Our preliminary results have led to the development of an elegant model that requires just two parameters to account for light adaptation over a range of luminances of greater than 105. Measurements will be aimed first at adaptation in M and L-cone pathways, and then at adaptation in short-wavelength (S) cone and rod pathways. Our results, we believe, will: (I) force a radical reappraisal of the way in which color-opponent and luminance signals are assumed to interact, lead to a more realistic psychological model of the organization of the early visual system, and require modifications to current models of the luminance channel; and (II) allow a critical reassessment and reformulation of models of light adaptation. In each case, we will relate our results to, and be guided by, the underlying retinal physiology and anatomy. Present knowledge of physiology and anatomy reveals a more complicated system than the canonical psychophysical model of luminance and chromatic channels. Our work, which identifies complex flicker interactions between fast and slow signals from the three cone types that are also seen in records from macaque ganglion cells will provide a link to current physiological and anatomical studies, and, we hope, motivate new ones.